Thus far we have shown that the S6 tubulin dimer is the component most sensitive to ionizing radiation in a polymerization competent preparation of microtubular protein. We thus propose to do the following: 1. Identify the molecular lession in the S6 component caused by irradiations; 2. Examine the effects of irradiation on intact microtubules; 3. Examine the functional capacity of tubulin isolated from irradiated tissue culture cells.